This invention relates to improvements in a fail-safe system in an electronic control system for an engine, and more particularly to the fail-safe system in which a fail-safe condition can be suitably accomplished.
Most automotive vehicles are equipped with an electronic control system which electronically controls an engine power output system including an internal combustion engine. The engine includes a device for causing the engine to generate an engine power output, for example, one relating to fuel injection control (such as an electronically controlled throttle device, or a fuel injector valve), one relating to spark timing control (such as s spark plug), and one relating to idling engine speed control (such as an auxiliary air control valve).
The electronic control system is usually provided with a fail-safe system which is adapted to put the engine power output causing device into a fail-safe condition or mode when it is detected that an abnormality or trouble arises in the engine power output causing device. In such the fail-safe condition, for example, the engine power output is lowered by fixing the opening degree of a throttle valve of the electronically controlled throttle device to a certain small level, by minimizing a quantity of fuel injected from the fuel injector valve, or by retarding the spark timing of the spark.